1. Field of the Invention
The present invention relates to a insert with a replaceable cutting edge. More specifically, the present invention relates to a replaceable-blade cutting insert and corner milling cutter with replaceable cutting edge using the same, in which the squareness of the cut corner and the flatness of the vertical wall of the cut corner are improved. The corner milling cutter of the present invention also includes end mills with replaceable cutting edges.
2. Description of the Background Art
Among widely known corner milling cutters, there are ones in which a cutting section is formed as an insert with a replaceable cutting edge (Japanese Laid-Open Patent Publication Number 2003-266232, Japanese Laid-Open Patent Publication Number 2004-291205, and the like). In the corner milling cutter with replaceable cutting edge described in Japanese Laid-Open Patent Publication Number 2003-266232, a parallelogram negative insert is mounted on a base positioned at an outer perimeter of an end of a main cutter body, with the side surface forming the rake face and the end surface (either the upper or lower surface) forming the outer perimeter flank face. In this type of cutter, the use of a parallelogram or trapezoid insert makes it possible to provide a positive axial rake. Since the flank face is formed at the outer perimeter flank face, the radial rake has to be a negative angle.
A negative radial rake, however, reduces the cutting quality of the cutter. To overcome this, Japanese Laid-Open Patent Publication Number 2004-284010 describes a cutter insert in which the base unit is twisted around two axial lines. In the cutter insert in Japanese Laid-Open Patent Publication Number 2004-284010, a height offset is formed at the ceiling surface or the base surface forming the rake face toward the corner side, thus providing a positive radial rake angle by providing a flank angle on the outer perimeter flank face. A similar cutter insert is also disclosed in WO2005/075135.
Referring to FIGS. 11A-11D, the problems involved with corner milling cutters that use rhombus chips will be described. In the cutter in FIG. 11, a rhombus insert 20D is mounted at the outer perimeter at the end of a main cutter body 31 so that the axial rake γp is positive, the radial rake γf is negative, the face angle (front cutting section angle) κ′ is positive, and the approach angle Ψ is positive. When the insert 20D is sloped so that an end point P2 of a ridge line 7 forming the main cutting section passes through the same circle as a path circle S of an end point P1, the sections of the ridge line 7 excluding its ends pass positions outside of the path circle S. As shown in FIG. 11D, the amount by which the ridge line 7 departs from the path circle S is greater toward the center of the ridge line. As shown in FIG. 12, a wall surface wf of a workpiece A cut by the ridge line 7 will form a surface that is expanded toward the middle, thus reducing the squareness of the cut corner.
Japanese Laid-Open Patent Publication Number 2004-291205 describes a technology that allows an insert to be tilted in a direction where the approach angle Ψ is a positive angle. As shown in FIG. 11, by having a positive angle for the approach angle Ψ, the end point P2 of the ridge line 7 can be positioned on the path circle S and the path of the main cutting section can be made to approach a direction that would be parallel with the axial line of the cutter.
This method, however, cannot overcome the problems described above.
Also, Japanese Laid-Open Patent Publication Number 2004-284010 and WO2005/075135 do not appear to make a special effort to improve the flatness of the wall surface of the workpiece or the squareness of the cut corner. The same applies to Japanese Laid-Open Patent Publication Number 2003-266232. As described in Japanese Laid-Open Patent Publication Number 2004-284010 and WO2005/075135, in a cutter with a height offset at the rake face so that the surface position is higher toward the corner and a radial rake that can be set up as a positive angle, inferior flatness of the wall surface of the workpiece and squareness of the cut corner becomes more prominent.